The most immediate political consequence of the massacre of nine people in Charleston's historic Emanuel African Methodist Episcopal Church has been a backlash against the alleged killer's most cherished symbol.

South Carolina Gov. Nikki Haley, in announcing her support for the removal of the Confederate flag currently flying on the State Capitol grounds, said Roof had a "sick and twisted" view of the flag. In truth, Roof's understanding of the flag's meaning is the correct one. The flag is an emblem of white supremacy, and always has been.

And in South Carolina and elsewhere, the campaign to remove the flag from government facilities has itself provoked a backlash. Speaking to Politico, South Carolina Republican state Sen. Lee Bright complained that protesters were denigrating the memory of Confederate soldiers: "These are honorable men who fought for their homes, their home state; to disgrace them in the name of political correctness is just wrong. They're not here to defend themselves."

In truth, something close to the opposite is happening. As historian David Blight writes in his 2001 book Race and Reunion, in the aftermath of the Civil War and Reconstruction, former Confederates and their supporters waged a propaganda campaign to shape American historical memory. The result was a popular understanding of the war and its aftermath that glamorized the valor of Confederate soldiers, downplayed slavery as a cause of the war and cornerstone of the Confederacy, recast Reconstruction as a period of tyranny and "black domination," and justified the violent disenfranchisement and dispossession of black Americans for decades to come.

Even after the narrative of a benign and honorable Confederacy fell out of favor with historians, it continued to dominate American popular culture in film and literature, from The Birth of a Nation to The Dukes of Hazzard. The damage wrought by this interpretation of history is immeasurable. It is only now unraveling.

Most important, it was always untrue: Slavery was the cause of the war, white supremacy was the cornerstone of Confederate society, the individual valor of Confederate soldiers cannot hide that the cause for which they fought was one of the worst in human history, their defeat was not solely due to the North's structural advantages, and they -- not the Union -- were the aggressors. Though taking down the Confederate flag may itself be of little practical consequence, the backlash against the stars and bars is a result of a monumental shift in popular memory that has the potential to shape our politics just as the Lost Cause once did.

Shortly after the war, Blight writes, former Confederate Gen. Jubal Early gained control of the Southern Historical Society and used it to "launch a propaganda assault on popular history and memory." Later groups like the United Confederate Veterans and the United Daughters of the Confederacy worked to "control historical interpretation of the Civil War." In this interpretation, popularly known as "Lost Cause" mythology, the Confederacy was fighting for some vague conception of liberty, not the right to own slaves; its soldiers were unparalleled warriors defending their homeland who were only defeated because of the Union's structural advantages; and the postwar subjugation of black Americans was a necessary response to lawlessness. Professional historians like those of the late 19th/early 20th century Dunning School bolstered the popular perception that granting equal rights to black Americans after the war was an immoral and tragic error, thus justifying the imposition of racial apartheid in the South.

If political correctness is the suppression of uncomfortable truths in order to avoid offense, then the American popular perception of the Civil War and its aftermath is the result of one of the most effective and devastating campaigns of political correctness in American history. The reversal of the popular understanding of the war and Reconstruction is possible only through the hard work of historians and popular writers like Ta-Nehisi Coates bringing their findings to a broader audience.

Hundreds of people protest against the Confederate flag during a protest rally in Columbia, South Carolina, on June 20, 2015.

Though there were intellectuals like W.E.B. Du Bois who challenged this interpretation of the Civil War and its aftermath, the interpretations of those like the Dunning School persisted long after their flaws were exposed by historians. "The writings of the Dunning School[...]offered scholarly legitimacy to the disenfranchisement of southern black Americans and to the Jim Crow system that was becoming entrenched as they were writing," historian Eric Foner wrote in The Dunning School, a 2013 anthology of essays on their influence.

Crucially, as Blight writes, this interpretation of the war and Reconstruction fostered a national reconciliation between North and South on terms that sacrificed black freedom to white supremacy.

"The general white public, the national leadership of the Republican Party, and the federal government on every level were arriving at the conclusion that African Americans did not merit citizenship and that their freedom was not valuable enough to justify the conflicts they engendered among whites," wrote historian Douglas Blackmon in Slavery by Another Name. This historical interpretation provided the moral underpinnings for Jim Crow and the brutal neo-slavery of the convict leasing system, and even today shapes our understanding of persistent racial inequality as the result of black Americans' personal failings rather than decades of government policy designed to exclude us from the benefits of American citizenship.

The North's acquiescence to this purging of historical memory is an essential part of this story. It is not only the sins of the South that must be reckoned with. Though the South fought to preserve and expand slavery, there were few racial egalitarians in the North, which is why the Lost Cause could so effectively shape popular understanding. The Unionist coalition was bigger than the secessionist coalition, but the white supremacist coalition, North and South, dwarfed both of them until the middle of the 20th century.

This is how the Confederate flag could become, in the minds of its supporters, something other than the banner of a racist slave empire, even though officials from states like Louisiana declared that "the people of the slave holding States are bound together by the same necessity and determination to preserve African slavery." If the Confederacy were in fact fighting for freedom and not in defense of bondage, then the stars and bars could mean something other than a cause for which Southerners should be ashamed.

Yet the Confederate flag's emergence in the mid-20th century was premised on the same strange interpretation of liberty as the one Confederate soldiers fought to defend. According to a 2000 report by the state of Georgia on the history its own flag, the stars and bars became "at least in part, if not entirely, a symbol of resistance to federally enforced integration." As the Confederates fought for the freedom to own slaves, so the Dixiecrats and their allies fought for the freedom to strip black Americans of theirs.

Only through the embrace of the Lost Cause is the interpretation of the flag as a benign symbol of Southern pride sustainable. But this reckoning with history as it was will no doubt be painful. The realization that a closely held truth is false always is. Greg Stewart, a member of the Sons of Confederate Veterans, told the New York Times, "You're asking me to agree that my great-grandparent and great-great-grandparents were monsters."

We are in no position to judge the souls of hundreds of thousands of men long dead. But to judge their cause is a simple matter, and their cause was monstrous. And whatever the anguish of white Southerners over this re-evaluation of the past, it pales in comparison to the trauma wrought by the lionization of the Confederacy.

"We are sometimes asked, in the name of patriotism," said Frederick Douglass in 1871, "to forget the merits of this fearful struggle, and to remember with equal admiration those who struck at the nation's life and those who struck to save it, those who fought for slavery and those who fought for liberty and justice."

Once we chose to forget. We are now choosing to remember.

Adam Serwer is the national editor for BuzzFeed News and is based in Washington, D.C. His secure PGP fingerprint is 883A 7AB8 4736 1BB9 A061 D26A F2B5 71C0 391A 0252